CMakePM: Use junctions for source/build dirs on Windows

This way we have fixed small (max 64 bytes) paths for CMake's configure
/ build / install steps.

This allows the user to have longer paths and still compile with MSVC /
GCC MinGW compilers.

Fixes: QTCREATORBUG-26786
Task-number: QTBUG-117413
Change-Id: I0cff6521626dd2ce78d0223d46f0b480e977d5c5
Reviewed-by: <github-actions-qt-creator@cristianadam.eu>
Reviewed-by: Alessandro Portale <alessandro.portale@qt.io>

src/plugins/cmakeprojectmanager/cmakeprocess.cpp

@@ -8,6 +8,7 @@
 #include "cmakeprojectconstants.h"
 #include "cmakeprojectmanagertr.h"
 #include "cmakespecificsettings.h"
+#include "cmaketoolmanager.h"
 
 #include <coreplugin/progressmanager/processprogress.h>
 #include <projectexplorer/buildsystem.h>
@@ -144,7 +145,10 @@ void CMakeProcess::run(const BuildDirParameters &parameters, const QStringList &
     });
 
     CommandLine commandLine(cmakeExecutable);
-    commandLine.addArgs({"-S", sourceDirectory.path(), "-B", buildDirectory.path()});
+    commandLine.addArgs({"-S",
+                         CMakeToolManager::mappedFilePath(sourceDirectory).path(),
+                         "-B",
+                         CMakeToolManager::mappedFilePath(buildDirectory).path()});
     commandLine.addArgs(arguments);
 
     TaskHub::clearTasks(ProjectExplorer::Constants::TASK_CATEGORY_BUILDSYSTEM);